I wanted to find out:
1.what is the latest version of unity that is out there right now?
2.what is the most stable and recommended version of unity?
I'd say Untiy 4.2(1) for both Question 1 and 2.
Here is the doc for info about the latest Unity version:
Also, if you can provide more info about the the backend Message store (Exchange or Domino), with /without failover, can give you more specific info